A Mutation in Amino Acid Permease AAP6 Reduces the Amino Acid Content of the Arabidopsis Sieve Elements but Leaves Aphid Herbivores Unaffected.

The aim of this study was to investigate the role of the amino acid permease gene AAP6 in regulating phloem amino acid composition and then to determine the effects of this altered diet on aphid performance. A genotype of Arabidopsis thaliana (L.) was produced in which the function of the amino acid permease gene AAP6 (At5g49630) was abolished. Plants homozygous for the insertionally inactivated AAP6 gene had a significantly larger mean rosette width than the wild type and a greater number of cauline leaves. Seeds from the aap6 mutant were also significantly larger than those from the wild-type plants. Sieve element (SE) sap was collected by aphid stylectomy and the amino acids derivatized, separated, and quantified using Capillary Electrophoresis with Laser Induced Fluorescence (CE-LIF). In spite of the large variation across samples, the total amino acid concentration of SE sap of the aap6 mutant plants was significantly lower than that of the wild-type plants. The concentrations of lysine, phenylalanine, leucine, and aspartic acid were all significantly lower in concentration in the aap6 mutant plants compared with wild-type plants. This is the first direct demonstration of a physiological role for an amino acid transporter in regulating SE composition in vivo. The amino acid availability in sieve element sap is thought to be the major limiting factor for aphid growth and reproduction. Despite the changes in their diet, the aphid Myzus persicae(Sulzer) displayed only small changes in feeding behaviour on mutant plants when measured using the Electronic Penetration Graph (EPG) technique. Salivation by the aphid into the SE (E1 phase) was increased on mutant plants but there was no significant effect on other feeding EPG behaviours, or in the rate of honeydew production. Consistent with the small effect on aphid feeding behaviour, there was only a small effect of reduced sieve element amino acid concentration on aphid reproduction. The data are discussed in relation to the regulation of phloem composition and the role of phloem amino acids in regulating aphid performance

Ring inversion in 1,1-Dibenzylcyclohexanes

In a recent communication, the barrier to chair-chair interconversion in 1,1 -dimethyl-4,4-dibenzylcyclohexane (1a) was reported from studies of carbon and proton magnetic resonance spectroscopy to be at least 20 kcal/mol. This observation was surprising in terms of what is known about inversion barriers in cyclohexane and was rationalized in terms of hindered rotation of the benzyl groups

Hydrodesulfurization of thiophene, benzothiophene, dibenzothiophene, and related compounds catalyzed by sulfided CoO-Mo3/gamma-Al2O3 : low-pressure reactivity studies

Hydrodesulfurization experiments were carried out with a sulfided CoO---MoO3/¿-Al2O3 catalyst in a pulse microreactor operated at atmospheric pressure and temperatures of 350 to 450 °C. The reactants were hydrogen and pure sulfur-containing compounds (or pairs of compounds), including thiophene, benzothiophene, dibenzothiophene, several of their hydrogenated derivatives, and various methyl-substituted benzothiophenes and dibenzothiophenes. The aromatic compounds appeared to react with hydrogen by simple sulfur extrusion; for example, dibenzothiophene gave H2S + biphenyl in the absence of side products. The reactivities of thiophene, benzothiophene, and dibenzothiophene were roughly the same. Each hydrogenated compound (e.g., tetrahydrothiophene) was more reactive than the corresponding aromatic compound (e.g., thiophene). Methyl substituents on benzothiophene had almost no effect on reactivity, whereas methyl substituents on dibenzothiophene located at a distance from the S atom slightly increased the reactivity, and those in the 4-position or in the 4- and 6-positions significantly decreased the reactivity. In contrast to the observation of a near lack of dependence of low-pressure reactivity on the number of rings in the reactant, the literature shows that at high pressures the reactivity decreases with an increased number of rings. The pressure dependence of the structure-reactivity pattern is suggested to be an indication of relatively less surface coverage by the intrinsically more reactive compounds (e.g., thiophene) at low pressures but not at high pressures. The relative reactivities are also suggested to be influenced by differences in the structures of the catalyst at low and high hydrogen partial pressures, which may be related to the concentrations of surface anion vacancies and the nature of the adsorbed intermediates